1. The Field of the Invention
The present invention is related to device and method for correcting a color distortion on a TV receiver, which can prevent a color distortion generated in reproduction of a color.
2. Description of the Related Art
FIG. 1 illustrates general transmission paths of a broadcasting signal, referring to which a process of a TV broadcasting signal transmission will be explained.
The TV broadcasting signal may be transmitted to a TV receiver 14 at a reception antenna 14A, taking both a direct path C1 and indirect path C2 and C3, such as a mountain 12 and a large building 13. A channel with plural broadcasting signal transmission paths is called a multi-path channel. Since a field intensity of the broadcasting signal received at the TV receiver 14 through the direct path C1 is high, the broadcasting signal is displayed on a screen bright and clear, while a field intensity of the broadcasting signal received at the TV receiver 14 through the indirect path C2 or C3, i.e., a ghost, is low, the broadcasting signal is displayed on a screen hazy. The ghost in an actual broadcasting channel appears, not only as a difference of brightness simply, but also various forms, such as a color distortion and an orthogonal distortion. 14B shown on the TV screen is a normal image, and 14C is a ghost. The ghost can be expressed with three parameters of a delay time, an attenuation constant, and a phase shift. The time delay, a parameter for representing a reception time difference of the broadcasting signal depending on a difference of path distances, is represented in a relative time difference of signal arrival with reference to a signal received through a main path in .mu.sec units. A ghost with a delay time less than "0" is called a full ghost, and a ghost with a little delay time compared to the main signal is called a near ghost. The near ghost in general is a ghost occurred near the main signal with 1.about.2 .mu.sec. and most of the ghosts we see in general ambient are these type of ghosts. The attenuation constant represents a degree of intensity of a signal through an indirect path with respect to a signal through a main path, i.e., an intensity of a signal compared to the main path. Phases of signal carriers through different paths in the multi-oath channel differ from a phase of a main path signal carrier, which is represented as the parameter of phase shift.
As can be known from the ghost parameters, the ghost is dependent on time, broadcasting environment, and broadcasting channel. Conditions of ghost generation vary depending, for example, reflection characteristic changes of reflecting bodies depending on environments, carrier frequencies transmitted from broadcasting stations, and the like, according to which a form of ghost is also changed. Therefore, in order to correct a color distortion coming from the multi-path channel, an adaptive feature is required. The color distortion is caused by a phase shift of a color subcarrier due to a ghost coming from a multi-path channel. As color information is carried on a phase in current TV broadcasting system, the greater the phase difference, the greater the color distortion.
In a study, it is found that the ghosts in general arc mostly distributed as near ghosts with 1.about.2 .mu.sec delay times, and almost all within delay times between -2.mu.sec and 20 .mu.sec. Therefore, a device for correcting a color distortion should be capable of correcting color distortions caused by ghosts with delay times of such a range. Efforts for improving a color degradation caused by the multi-paths in a TV signal transmission have mostly been concentrated on an apparent particular color of color signals. However, these techniques could not correct color distortions generated by the multi-path perfectly. And, recently researches for canceling ghosts generated by the multi-path channel in a more fundamental fashion are already underway, and some of which are available as commercial products.
However, though ghosts are canceled and colors are restored by compensating the multi-path channel characteristic itself, because such ghost canceling means employs a long transverse filter and an exclusive signal processor, it has a limitation in reducing a hardware cost.
Of color signals, because such background art color distortion correcting means are adapted to correct colors with reference to a particular color apparent to eyes, they can not correct the color distortions generated by a multi-path channel, fundamentally.
And, though ghosts are canceled and colors are restored by compensating the multi-path channel characteristic itself by using a ghost canceling means which can cancel ghosts generated by a multi-path channel recently, because such ghost canceling means employs at long transverse filter and an exclusive signal processor, it has a defect of requiring much hardware cost.